Volume control



y 9, 1939. K. MULLER 2,157,557

VOLUME CONTROL FilediNov. 17, 1936 INVENTOR KURT MULLER BY Kim ATTORNEY Patented May 9, 1939,

PATENT OFFICE VOLUME CONTROL Kurt Miiller, Berlin-Siemensstadt, Germany, as-

signorto Siemens & Halske, Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany Application November 1'1, 1936, Serial No. 111,239

In Germany November 14, 1935 5 Claims The present invention -relates generally to volume control devices and more particularly to a combined series resistor and potentiometer device.

5 Volume control means are frequently used in the broadcast receiving arts, especially in the AF stages, in order that the desired acoustic intensity of the loudspeaker may be secured. However, in addition to their regulating function, control'means of the said sort must also possess the property that the adaptation to the output end of the amplifier with which it is to be operated, is varied inside the smallest possible limits. For if certain prearranged limits of rel5 sistance value were exceeded, this would be conducive to serious distortion.

In connection with volume control problems of loudspeakers it has already been known in the art to provide attenuation networks of T or H shape with variable damping whose input re sistance, with a proper end or terminal, stays perfectly constant, and in which the volume may be regulated by stages or steps. impedance of the loudspeaker itself does not stay constant; still, sufficient constancy of the input resistance is obtainable with these attenuation networks, although they inhere the serious drawback that they comprise quite a number of resistances and multi-contact switches. As a result, they are rather expensive in construction, and their regulation is not continuous.

But a simple potentiometer circuit organization can not be used for two reasons. In the first place the change in the input resistance is too great seeing that the potentiometer can not be made of high ohm value; in the second place, this is always attended with a loss of energy seeing that even in the end position where the sound volume is of maximum value, potentiometer and loudspeaker are connected in parallel so that they represent resistances of like order of magnitude.

Now, this invention discloses a sound volume control, more particularly a loudspeaker regulator in which a switch is so united with a regulating resistance or rheostat that the input resistance of the aggregate arrangement will vary only within pre-fixed limits. The regulating resistance in this scheme, in one position of the switch,

is connected so as to act as a regulable series resistance, and in the other position as a potentiometer. With the resistance the switch is connected in series, and the switch is so operated from 'the rotating shaft of the resistance that the contact will be either closed or opened acment of the invention showing the position of To be sure, the

cording to a prearranged adjustment of the resistance tap between the end positions thereof.

In what follows an exemplified embodiment of the basic idea of the invention is described in connection with the drawing wherein Fig. 1 is a 5 diagrammatic showing of the invention in connection with a loudspeaker circ'uit; Fig. 2 is a curve sheet used in illustrating the operation of the invention; and, Fig. 3 is a preferred embodi- 10 the switching means with respect to the resistor element.

The circuit organization represented in Fig. 1 comprises a potentiometer. P and in series therewith a switch S being connected at point E. Connected with the tap of the potentiometer is the loudspeaker L. The potentiometer whose resistance variation preferably follows a logarithmic law is combined with the switch so as to form a construction unit, the switch cam being so set that the switch is closed when the tap is in a position between the beginning and the end (A and E) of the potentiometer, say, at K. In a certain position of the tap between" A and K, as shown in the figure, the switch S will then be opened. This means that the potentiometer from position A up to the maximum position at K serves merely as a series resistance, so that no resistance is connected in parallel to the loudspeaker. From point K as far as E the potentiometer then acts as such, and then the acoustic volume may be reduced down to almost zero.

The following numerical example shows the practical advantage in actual operation of 'the invention as regards adaptation or matching to an amplifier tube. The output of an amplifier, as well known, allows only resistance variations within very narrow limits, say, between 130 and 200 ohms. If, accordingly, the aggregate resistance AE is chosen at 200 ohms .and the par- 40 tial resistance AK= ohms, in the presence of a loudspeaker resistanceof 140 ohms, there results a minimum resistance of ohms and a maximum resistance of 200 ohms. Fig. 2 shows the curve of the input resistance which, in the 5 present instance, starts at ohms, which then. rises progressively to 200 ohms, and which then falls to 130 ohms, whereupon it rises again continuously. In other words, an arrangement as here disclosed insures largely adaptation or 50 matching to the amplifier, in the presence of a gradual regulation of the sound volume between zero and the aggregate value of available energy.

What should particularly be mentioned is that by the closing of the switch no inadmissible cracking in the loudspeaker may be produced by actuation of the switch inasmuch as the change in potential prevailing at the loudspeaker by the switch occurs only at the ratio 1:1.3 so that it will be hardly audible;

Fig. 3 shows schematically an instance of the construction of the resistance-switch unit. On the same shaft as the resistance tap is the switch cam N1 which, in a pre-arranged position of the tap actuates the cam N2 being associated with the contacts.

What is claimed is 1. In signalling circuits, a source of signal energy including a pair of output terminals, a reproducer having a pair of input terminals, a

resistance element having one end thereof connected to one of said output terminals, a variable tap on said resistor element, means for connecting one of the input terminals of said reproducer to said variable tap, means for connecting said other output terminal to the other reproducer input terminal, a switch adapted to connect said resistor element across said two output terminals and coupling between said variable tap and switch for operating said switch when said tap is operated along a predetermined portion of the resistance element.

2. An adjustable attenuating system adapted to be interposed between a source of signal energy and a translating device comprising, a resistance element shunted across said. source, a variable tap adapted to be operated along said resistance element, means for connecting the translating device between the variable tap and one end of the resistance element, operable switching means for disconnecting from the source of signal energy the end of the resistance to which the translating device is connected, and means for controlling said switching means in accordance with the operation of the variable tap.

3. An adjustable attenuating system adapted to be connected between a source of signal energy and a translating device comprising, a resistance element adapted to be connected across the source through a switching means, a variable tap on said resistance element adapted to be moved along the range of the resistance element, a translating device connected between said variable tap and said source, and means controlled by said variable tap for operating said switch means so as to close the switchwhen the variable tap is positioned along a portion of said range and to open the switch when the variable tap is positioned along another portion of said range.

4. In a variable coupling device, an input terminal, an output terminal and a common terminal, a resistor and an operable switch in series connected between the input terminal and the common terminal in the order named, a utilizing circuit connected between the output terminal and the common terminal, a variable tap adapted to operate along said resistor element, means for connecting the variable tap to said output termiha], and coupling meansbetween the variable tap device and said switch for operating said switch.

5. A volume control device adapted to be interposed between a source of signal energy and a utilizing device comprising, a circuit connected across the source of signal energy and including a resistance element and an operable switching means in series, a variable contact device adapted to operate along said resistance element, means for connecting the utilizing device between the contact device and the switch end of said first named circuit, and coupling means between the switch and the variable contact means and effective upon the operation of the variable contact means past a predetermined intermediate point of said resistance element for closing said switch in one direction of travel of the contact means along said resistance element and to open said switch in the opposite direction of travel of the contact means along the resistance element.

KURT Mi'ILLER. 

